Electro-stimulated tribological behavior of DLC coatings under unlubricated sliding conditions

As EV systems evolve, higher demands are placed on the reliability and sustainability of tribological components operating under combined mechanical and electrical stresses. Electrical damage arises when stray currents pass through bearing contacts, leading to electrical arcing, pitting, and surface degradation of rolling elements and raceways. DLC coatings, due to their low friction characteristics and inherent dielectric properties, are promising for electrically stressed environments. However, their tribological behavior under direct electrical stimulation remains insufficiently understood, especially in DLC/steel contacts. This study investigates the effect of applied direct current (0–2 A) on the dry sliding behavior of hydrogenated-DLC (H-DLC), tetrahedral amorphous carbon DLC (H-free DLC), and uncoated steel against a steel ball in ball-on-disk tribometer under ambient conditions. H-DLC exhibited ultralow coefficient of friction (COF ≈ 0.05) and minimal wear at low current (0.1 A), attributed to the formation of a hydrogen-assisted graphitic tribolayer. In contrast, H-free DLC and steel showed comparable or increasing friction and wear with rising current. At currents ≥ 1 A, all materials experienced tribolayer breakdown with oxidation and surface degradation. These findings demonstrate that electric current can act as a tribo-chemical activation mechanism, with the response being strongly dependent on the coating material properties and structure.